I went into the big propane
dealer, in the center of town, near where I used live. They were re-certifying propane
tanks of all sizes and ages. Lots of them there with a full time guy doing the work. So I wandered over to see the process. Very simple really, just a low wage, unskilled worker with a wire wheel on a hand grinder. He'd simply remove all the paint
with the wire wheel, re-stamp the cylinders, paint
them and out they'd go for another life cycle. That's it. No hydro test or careful inspection.
Then one day I was at a local RV dealer. A guy came in with a full 20 lb cylinder that he wanted to re-cycle. He asked if they could help him. "Sure, no problem".
The worker simply set the bottle down where he was working, right in the middle of everything, cars, equipment and a busy street just a few feet away, and opened the valve wide open to drain it. Whoosh! A huge vapor cloud
enveloped the place! Yikes!, let me outta here, was my reaction. Sheesh.
It's not really fair to compare propane tanks with oxygen
might have close to 5,000 PSI whereas propane is only about 70. Propane bottles have a very good guard around the valves too.
I blew up an oxygen bottle one time just for fun and to see how it failed. I raised the internal pressure until it ruptured. It was spectacular. It split it's entire length and most of the way around each end, flattened out and left both ends hanging on by about a 1" strip of metal. Plus it flew a long way in the process. Very impressive!